Coherent collective behavior fascinates us when a global pattern emerges from
individuals who share information with others only in their local vicinity.
Decisions made by one individual apparently cascade throughout the entire
group. That said, not all members have the same influence. The challenge here
in explaining such emergent behaviors is to infer the underlying relationships
among individuals from observations. Not surprisingly, this challenge has
attracted many over decades to diagnose collective behaviors in a variety of
systems
[1]}, [2]}, [3]}, [4]}, [5]}, [6]}, [7]}.
In epithelial Madin-Darby canine kidney monolayers, for example, collective
cell migration is triggered by multicellular protrusions forming a fingerlike
structure [8]}, [9]}, [10]}. Photoablating a group of
cells from the finger tip makes the remaining cell group lose its sense of
direction. The interpretation is that the former and latter cells have acted as
if they were “leaders” and “followers”. This functional assignment can be
carried out due to their spatial location along the protrusion and since the
two cell classes are genetically distinct [10]}.
